For environmental assessment of contaminated sites ecotoxicity tests shall involve more environmental elements and the tests shall be conducted with test organisms from several trophic levels. Bacillus subtilis, a moderately sensitive bacterium to toxic metals, is suitable for the assessment of metal contaminated sites. A sample disc solidified with agar is prepared from the environmental element (soil, groundwater) originating from the contaminated site and it is placed onto the surface of the nutrient agar inoculated with the test organism. The contaminant is diffused from the sample disc to the agar plate and depending on its concentration and toxicity it inhibits growth of microorganisms. The inhibition is indicated by the low density concentric zone around the sample disc. The methodology is described in the ENFO database: https://www.enfo.hu/en/node/13311